Destruction of WiDr multicellular tumor spheroids with the novel thymidylate synthase inhibitor 1843U89 at physiological thymidine concentrations

Experimental anti-tumor therapy in 3-D: spheroids--old hat or new challenge?

PURPOSE

To give a state-of-the-art overview on the promise of three-dimensional (3-D) culture systems for anticancer drug development, with particular emphasis on multicellular tumor spheroids (MCTS).

RESULTS AND CONCLUSIONS

Cell-based assays have become an integral component in many stages of routine anti-tumor drug testing. However, they are almost always based on homogenous monolayer or suspension cultures and thus represent a rather artificial cellular environment. 3-D cultures--such as the well established spheroid culture system--better reflect the in vivo behavior of cells in tumor tissues and are increasingly recognized as valuable advanced tools for evaluating the efficacy of therapeutic intervention. The present article summarizes past and current applications and particularly discusses technological challenges, required improvements and recent progress with the use of the spheroid model in experimental therapeutics, as a basis for sophisticated drug/therapy screening. A brief overview is given focusing on the nomenclature of spherical 3-D cultures, their potential to mimic many aspects of the pathophysiological situation in tumors, and currently available protocols for culturing and analysis. A list of spheroid-forming epithelial cancer cell lines of different origin is provided and the recent trend to use spheroids for testing combination treatment strategies is highlighted. Finally, various spheroid co-culture approaches are presented that have been established to study heterologous cell interactions in solid tumors and thereby are able to reflect the cellular tumor environment with increasing accuracy. The intriguing observation that in order to retain certain tumor initiating cell properties, some primary tumor cell populations must be maintained exclusively in 3-D culture is mentioned, adding a new but fascinating challenge for future therapeutic campaigns.

Pharmacokinetics, Safety, and Efficacy of a Liposome Encapsulated Thymidylate Synthase Inhibitor, OSI-7904L [(S)-2-[5-[(1,2-Dihydro-3-methyl-1-oxobenzo[f]quinazolin-9-yl)methyl]amino-1-oxo-2-isoindolynl]-glutaric Acid] in Mice

OSI-7904L [(S)-2-[5-[(1,2-dihydro-3-methyl-1-oxobenzo[f]quinazolin-9-yl)methyl]amino-1-oxo-2-isoindolynl]-glutaric acid] is a liposomal formulation of the highly specific, noncompetitive, thymidylate synthase inhibitor OSI-7904 (also known as GW1843, 1843U89, and GS7904). The liposome formulation was developed to enhance the therapeutic index and dose schedule convenience of this potent antifolate compound. The studies presented here were conducted to determine the antitumor efficacy, distribution, pharmacokinetics, and safety of OSI-7904L in mice. In a human colon adenocarcinoma xenograft model in mice, OSI-7904L demonstrated superior antitumor efficacy compared with OSI-7904 or 5-fluorouracil. Furthermore, OSI-7904L could be administered less frequently than OSI-7904 although still generating greater tumor growth inhibition. Distribution studies confirmed that OSI-7904L-treated animals had much greater plasma, tissue, and tumor exposure than did OSI-7904-treated animals. Tumor exposures, based on area under the curve, in OSI-7904L-treated mice were increased over 100-fold compared with tumor exposures in OSI-7904-treated mice. Plasma exposures following OSI-7904L administration were greater than dose proportional consistent with saturation of plasma clearance mechanisms. OSI-7904L was much more toxic than OSI-7904 in the mouse with primary toxicities to the intestines, bone marrow, and thymus. Minimal toxicity to the lungs and liver was noted. These data clearly demonstrated that in mice, OSI-7904L has an increased plasma residence time as well as increased tissue and tumor exposure compared with OSI-7904, thus resulting in increased potency and toxicity. Potential benefits of OSI-7904L include improved efficacy and a more convenient schedule of administration.

Increases in Neutral, Mg2+-Dependent and Acidic, Mg2+-Independent Sphingomyelinase Activities Precede Commitment to Apoptosis and Are Not a Consequence of Caspase 3–Like Activity in Molt-4 Cells in Response to Thymidylate Synthase Inhibition by GW1843

Thymidylate synthase (TS) inhibition causes cell death, and this enzyme is the target for the important chemotherapy regime 5-fluorouracil/leucovorin. GW1843 (1843U89) is a potent and specific folate analog TS inhibitor in clinical development. Because of the importance of TS as a chemotherapy target, we are studying the mechanism of TS inhibition-induced cell death by GW1843. Ceramide is a regulatory lipid generated by the action of sphingomyelinase and is believed to signal apoptosis. The role of the ceramide in apoptotic signaling was studied in Molt-4 human T-cell leukemia cells undergoing cell death after treatment with GW1843. In response to GW1843, Molt-4 cells undergo apoptosis with both acidic pH, Mg2+-independent sphingomyelinase (ASMase) and neutral pH, Mg2+-dependent sphingomyelinase (NSMase) activities elevated as early steps in the initiation of apoptosis before Molt-4 commitment to death. These activities lead to ceramide production with kinetics consistent with a role as an effector molecule signaling the initiation of apoptosis in Molt-4 cells. These changes were found to be independent of caspase 3–like (CPP32/apopain) activity and DNA degradation, but were not separable from membrane blebbing or cell lysis in this cell line. In this report, kinetic evidence is provided for a role of ceramide in initiating GW1843-induced cell death of Molt-4 T-cell leukemia cells.

Increases in Neutral, Mg2+-Dependent and Acidic, Mg2+-Independent Sphingomyelinase Activities Precede Commitment to Apoptosis and Are Not a Consequence of Caspase 3–Like Activity in Molt-4 Cells in Response to Thymidylate Synthase Inhibition by GW1843

Thymidylate synthase (TS) inhibition causes cell death, and this enzyme is the target for the important chemotherapy regime 5-fluorouracil/leucovorin. GW1843 (1843U89) is a potent and specific folate analog TS inhibitor in clinical development. Because of the importance of TS as a chemotherapy target, we are studying the mechanism of TS inhibition-induced cell death by GW1843. Ceramide is a regulatory lipid generated by the action of sphingomyelinase and is believed to signal apoptosis. The role of the ceramide in apoptotic signaling was studied in Molt-4 human T-cell leukemia cells undergoing cell death after treatment with GW1843. In response to GW1843, Molt-4 cells undergo apoptosis with both acidic pH, Mg2+-independent sphingomyelinase (ASMase) and neutral pH, Mg2+-dependent sphingomyelinase (NSMase) activities elevated as early steps in the initiation of apoptosis before Molt-4 commitment to death. These activities lead to ceramide production with kinetics consistent with a role as an effector molecule signaling the initiation of apoptosis in Molt-4 cells. These changes were found to be independent of caspase 3–like (CPP32/apopain) activity and DNA degradation, but were not separable from membrane blebbing or cell lysis in this cell line. In this report, kinetic evidence is provided for a role of ceramide in initiating GW1843-induced cell death of Molt-4 T-cell leukemia cells.

Multicellular spheroids: a three-dimensional in vitro culture system to study tumour biology

The growth of tumour cells as three-dimensional multicellular spheroids in vitro has led to important insights in tumour biology, since properties of the in vivo-tumour such as proliferation or nutrient gradients, can be studied under controlled conditions. While this review starts with an update of recent data on spheroid monocultures, especially concerning tumour microenvironment and therapeutic modalities, the main emphasis is put on the spectrum of heterologous cultures which have evolved in previous years. This type of culture includes tumour cell interaction with endothelial, fibroblast or immunocompetent cells. The relation of the spheroid culture model to other types of three-dimensional culture and our critical evaluation and presentation of the technical aspects of growing and analysing spheroids are included in the text. These topics are chosen to help the experimental pathologist design experiments with tumour spheroids and to stimulate discussion.

Experimental chemotherapeutic agents for the treatment of colorectal carcinoma

Colorectal cancer is the third leading cause of cancer mortality for men and women in the United States. For the past 40 years fluorouracil has been the only agent with significant activity in this disease. More recently, advances in our understanding of the molecular biology of cancer have permitted the development of effective new agents for this disease. This article examines the current and future status of these new agents.